While recently blood NfL concentrations at baseline and at follow-up (mean of 6.4 years) were found to be higher in de novo PD patients compared to controls (Ma et al. 2021), others did not find a difference for earlier PD disease stages (means for age, H&Y and disease duration: 57 years/2.0/34 months) (Marques et al. 2019). This evidence concerns the gene NEFL and Parkinson disease.